Ground layout questions

[Phil_S]

I'm having a bit of a tough time with layout on a TWX. In particular, I'm not accustomed to the star ground, as I'm a big fan of buss ground. The various stars make perfect sense to me (except one), but the placement has me a bit flumoxed. Looking at Francesca pictures, it appears the KF just planted the star at any convenient spot. In my mind, this means the chassis is being used as a component rather than a shield. So, I'm not fond of this, but would appreciate some commentary on it.

How important do you think it is to have the buss soldered to the pots. In other builds, I've gotten a good result with a floating buss that lives physically between the board and the pots. Short runs of wire to the buss bar seem to work fine. Any reason I shouldn't do that?

The only full layout I've found is Ceriatone. I like to consult as much documentation as I can before building, but I don't believe everything I see. On that one, I see the bias supply ground point at the same spot as the green earth wire from the a/c wall supply. That just looks all wrong to me and I'm not going to do it.

Normally, I ground the bias supply with the B+ CT, the main filter caps, and the power tube cathodes.

Where would you ground the bias supply? I can't find it in any of the pictures as it seems to hide in a dark corner. I'm seeing that it probably goes to the same spot as the red/yellow CT wire, but can't be sure from the pix.

I see in the pictures, power tube cathodes are grounded to the tube socket bolt or is that a spot on the chassis near the tube socket. Is there any reason not to bring the power cathode grounds to the same point at the B+ CT?

Thoughts and comments are appreciated.

[paulruby]

Do it the way you're familiar with and have had good results.

Most important thing: make a very tight circuit loop of the PT, recto diodes, first filter cap and PT CT.

[CaseyJones]

Do it the way you're familiar with and have had good results.

Generally sound advice from a man with a reputation for sound advice but...

I'm a complete slob! My usual grounding scheme that works on low gain vintage amps ain't gonna cut it in this puppy!

Most important thing: make a very tight circuit loop of the PT, recto diodes, first filter cap and PT CT.

I got a better idea. Look inside one of Paul's amps and copy it EXACTLY!

[paulruby]

Copying mine is not a bad idea... Here's one to look at if you like. Click the pics for large versions.

http://paulrubyamplification.com/Marta.html

I use a buss ground. It doesn't matter if it is soldered to the pots, floating behind them or on the board (like mine).

Be sure your electrical ground is connected directly to the chassis at the input jack. Sometimes I use a non-isolated jack and sometimes I bolt a ground lug right next to the input jack. This ensures no radio comes in through your input wire.

First filter cap is mounted right at the PT. The PT CT goes directly to the negative of the 1st filter cap. Then jumper from here to the point where the power tubes will ground. Then jumper from here to where all other (preamp) grounds will be. A bus pretty much ensures you will follow this flow.

Bias ground should be at the same point as the PI and power tube grounds.

The original wreck layout also meets all the above... Using the chassis as a conductor is OK if you don't create ground loops. Using a bus tends to help ensure you don't create a ground loop but that doesn't mean a bus is required.

[Phil_S]

Hi Paul,
Thanks very much for confirming what I thought. I work on this in a bit of a vacuum and some consultation via a group like this is worth it's weight in gold. I built a JTM45 a while back using a buss and it's so quiet you can hear a mouse take a whiz. The 18watter by the same method has hiss but no hum. I've concluded a little hiss is characteristic of a high gain amp and must be the result of the sum of the components.

From the start, I've been inclined to go with the familiar buss method (it's really a long star). However, there seems to be a bit of superstition about the way this particular amp is built and being faithful to something. I'm already off the wagon. The iron is "non-standard" and the power tubes will be 6AQ5. I think I've worked out a way to shoehorn in the 6AQ5's at a reasonable plate voltage that won't fry them, and then to keep the pre-amp pretty darn close to the voltages reported on the "Kelly 90" schematic. Since I don't play out, I'm typically looking for a way to minimize the ear bleed level.

This will be my 8th build and the first with almost all new parts (not counting the Gilmore Jr. kit). I typically build with recycled iron and chassis, which saves a boatload of money, and gives countless hours of layout hell, which for me is entertainment.

I hope to have this one built by end of month. I'll report back.

Thanks again.

Regards,
Phil

[playonit]

Hey Paul, I notice in the pics you wrap most of your connects around the Turrets and not in the top holes of the turret. Is there a reason for doing it this way??

Thanks

[sliberty]

Phil,

When I built my UniWreck, Paul recommended the buss on the board approach to me too and it worked really well. I implemented it a little differently than his pictures show - see mine.

Steve

[doctord02]

Hey Paul, I notice in the pics you wrap most of your connects around the Turrets and not in the top holes of the turret. Is there a reason for doing it this way??

Thanks

I'm not Paul, but I'll hazard a guess; wrapping the turret guarentees a physical connection thats solid - the solder just makes sure its bonded. Depending on the solder alone to hold a component into the turret hole makes it prone to possible cold joints and vibration issues...

[Phil_S]

Steve,
That's about what I've got in mind. Like my 18W, here:
http://tinyurl.com/2deax9
I did the JTM45 like that, too, but the pix of it aren't as good.
Phil

[Phil_S]

Hey Paul, I notice in the pics you wrap most of your connects around the Turrets and not in the top holes of the turret. Is there a reason for doing it this way??
Thanks

I'm not Paul, but I'll hazard a guess; wrapping the turret guarentees a physical connection thats solid - the solder just makes sure its bonded. Depending on the solder alone to hold a component into the turret hole makes it prone to possible cold joints and vibration issues...

I agree that the wrap is better construction. I save the hole in the top for times when I can stuff it tight with 2 or 3 resistors or caps, or for pesky teflon coated stranded wire that won't stay put for a wrap (or is a hair too short).

[drhulsey]

I save the hole in the top for times when I can stuff it tight with 2 or 3 resistors or caps

If you make a v-shaped bend in your wire the is slight too big for the lumen of the turret, a single wire can achieve a physical bond within the turret. It's not as secure as a wrap, but you can invert your board without the component falling out

[sst4270]

Phil,

I used the "galactic grounding" scheme on my TWX per Kevin O'Connor's The Ultimate Tone Vol. 3.

You can find a gut shot of MaryBeth here:

https://tubeamparchive.com/viewtopic.ph ... t=marybeth

Just wanting to provide you with another alternative.

Hope it helps.

Steve

[sst4270]

Phil,

I used the "galactic grounding" scheme on my TWX per Kevin O'Connor's The Ultimate Tone Vol. 3.

You can find a gut shot of MaryBeth here:

https://tubeamparchive.com/viewtopic.ph ... t=marybeth

Just wanting to provide you with another alternative.

Hope it helps.

Steve